This application claims the benefit of Korean Patent Application No. 98-39100, filed Sep. 21, 1998, the entire disclosure of which is hereby incorporated herein by reference.
The present invention relates to the field of integrated circuits in general, and more particularly to charge coupled devices.
Solid state image pickup devices, such as Charge Coupled Devices (CCDs), can be relatively small, light weight, and consume less power than other image pickup type devices such as an electron gun. Therefore, it is known to use CCDs in broadcasting, domestic video cameras, monitoring camera systems, digital still cameras, and the like.
The CCD shown in FIG. 1 is arranged in the form of a charge coupled array that includes a horizontal transfer section 10. The horizontal transfer section 10 includes transfer gate electrodes 12 formed on an integrated circuit substrate such as a semiconductor substrate 11. An output gate electrode 13 is disposed adjacent to the last one of the transfer gate electrodes 12 on the semiconductor substrate 11. An n type impurity region 14 is formed in the semiconductor substrate 11 adjacent to the output gate electrode 13. The n type impurity region 14 is a floating diffusion region.
A reset gate electrode 16 is disposed between the floating diffusion region 14 and an n type impurity region 15. The n type impurity region 15 is formed in the surface region of the semiconductor substrate 11 adjacent to the reset gate electrode 16. The floating diffusion region 14, the n type impurity region 15 and the reset gate electrode 16 form a Field Effect Transistor (FET) 20.
In operation, the potential at the floating diffusion region 14 is reset to the voltage level VOD by application the reset signal xcfx86R. Signal charges are transferred from the array by the horizontal transfer section 10 and converted from signal charges into signal voltages in accordance with the respective variation of the input potential from the reset voltage level. In particular, clock signals xcfx86H applied at the output gate electrode 13 cause electrons (charge signals) to enter the floating diffusion region 14. The electrons are stored in the floating diffusion region 14 in accordance with the capacitance associated with the floating diffusion region 14.
The presence of the charge signals in the floating diffusion region 14 may 10 cause the voltage level thereon to be lowered compared with the initial reset voltage level which is provided by the reset signal xcfx86R. The output circuit 30 detects the lowering of the potential of the floating diffusion region 14 and outputs a corresponding voltage level. The voltage level at the floating diffusion region is reset by the application of the reset signal xcfx86R before reading the next charge signals.
It is known to use CCDs in situations having relatively low levels of illumination, wherein respective weak signal charges may need to be converted into signal voltages for output. Unfortunately, as the area occupied by the CCDs decreases, the capacitance of the floating diffusion region 14 may make it difficult to provide adequate signal voltages in situations involving low level illumination. Accordingly, there is a need to allow improved CCDs and methods of transferring charge signals in CCDs.
It is, therefore, an object of the present invention to allow improved charge coupled devices and methods of transferring charge signals from charge coupled devices.
It is another object of the present invention to allow charge coupled devices having increased sensitivity.
These, and other objects of the present invention, may be achieved by charge coupled devices that include an integrated circuit substrate and a transfer circuit, in the integrated circuit substrate, that transfers charge signals in the charge coupled device to provide transferred charge signals. An amplifier, in the integrated circuit substrate and electrically coupled to the transfer circuit, amplifies the transferred charge signals to generate amplified charge signals.
According to the present invention, the amplifier can provide improved sensitivity by amplifying the transferred charge signals. The amplified charge signals can be amplified by a gain factor (xcex2) of the amplifier. The sensitivity of the charge coupled device may also be increased by reducing the associated capacitance.
In another aspect of the present invention, the charge coupled device includes an output circuit, electrically coupled to the amplifier, that outputs the amplified charge signals from the charge coupled device.
In another aspect of the present invention, the charge coupled device includes a reset circuit, electrically coupled to the amplifier, that resets a level of the amplified charge signals in response to a reset signal applied to the reset circuit.
In one embodiment, the reset circuit is a field effect transistor that includes a drain region electrically coupled to a reset voltage level and a gate region electrically coupled to a reset signal line. A source region is electrically coupled to the amplifier and the n type semiconductor source region electrically couples the amplifier to the reset voltage level in response to a reset signal applied to the reset signal line.